Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

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C-ya
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Re: Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

Postby C-ya » Thu Sep 22, 2022 6:20 am

Wow, looks great. Quick turn-around, too. I'm guessing you have a local shop doing this? I have done some surface mount work, and one or two of those would be doable, but I wouldn't want to do much more than that.


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VStar650CL
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2004 Nissan Altima 2.5 S

Re: Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

Postby VStar650CL » Thu Sep 22, 2022 8:06 am

Yah, hand soldering is fine for protos if you're good with solder (which I am), but more than a couple is a job for the easy bake and not an iron. These will need special treatment if they go to any sort of production, though. You might notice the solenoid driver is a SOT23, so it needs a crapload of heat-sinking copper underneath it on the board for a 1A load. That means even high preheat and thermal-reliefs on the pads probably won't assure good joints in the oven. Only retouching with a very hot iron will serve.

I use Sunstone Circuits in Oregon for all my stuff, they're great. Gerbers in, boards out, untouched by human hands until they're packed for shipping. Zip zip.

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VStar650CL
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Re: Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

Postby VStar650CL » Thu Sep 22, 2022 7:07 pm

Good news and bad. Turns out the optimal PWM profile for the solenoid is about 10KHz at 35%, with a 7% safety margin for dropout. That's outstanding, it means a measly 5W will keep the thing lifted at an easy-peasy frequency. Bad news is here:
SOT23 Solenoid Drive.jpg
To translate the pic, the solenoid is switching "on" with the falling edge of the signal. Notice the slope in the edge, that's the SOT23 MOSFET struggling momentarily to pull a hard ground. That's because the FET is momentarily acting like a variable resistor, and just like any resistor, that makes it heat up. The proto confirms it, the FET steadies out at almost 60C even with all that copper underneath it. That wouldn't be a problem if the situation in the car was the same as the workbench, but it won't be. The unit will be potted and living in a relatively toasty engine box. So to be safe, the next spin will use a much bigger package with more dissipation and a lower RDSon, probably an IRLR8726. RDSon is "resistance drain to source" when switched on, and it's the primary determiner of how much waste heat a FET will generate at a given current level. The DMN3042 has an RDSon of about 22 milliohms at the solenoid's amperage, which might not sound like much, but Ohm says it will cause a minimum 330 milliwatts of waste heat and much more during that "slope". That's a lot for a SOT23 peashooter with a maximum dissipation of 720 milliwatts. The IRLR8726 is more like 8 milliohms and can dissipate 38 watts worst-case, so it will be coasting.

One other safety issue occurred to me, which is the possibility of an open sensor. Because of the fixed pullup, an open wire will make the sensor read cold and not hot. There's no easy architectural way around that with a standard automotive NTC sensor, so the next spin will do the next best thing, have the ground for the sensor controlled by the micro so it can detect an open circuit and shut down the solenoid. There are spare test pads on the proto boards, so for now I'll cut the sensor ground pads loose and run a jumper wire.

On to the next thing!

C-ya
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Re: Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

Postby C-ya » Fri Sep 23, 2022 9:38 am

Good luck with the changes. Sounds like they should work. How thick are you thinking of for the potting? Bare board with potting or potted inside a small case?

That is the thing with designing and testing. You always find something you didn't anticipate!

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VStar650CL
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2004 Nissan Altima 2.5 S

Re: Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

Postby VStar650CL » Fri Sep 23, 2022 10:08 am

Small case, with metal inserts potted in and drilled for attachment to the valve mounting screws. Except for the sensor (which needs to be remote), I'd like the whole valve-board-bracket to be an assembly.

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VStar650CL
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Re: Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

Postby VStar650CL » Sun Sep 25, 2022 7:44 am

C-ya wrote:
Fri Sep 23, 2022 9:38 am
That is the thing with designing and testing. You always find something you didn't anticipate!
Yah, it's axoimatic in engineering that's it's never the big, man-eating alligators that bite you in the a$$. You can see those coming. It's always the little, foot-long ones that sneak up and bloody your butt. Here's another one: Because of the way the ground bus on the proto boards was routed, I had to do quite a bit of fancy cutting and jumpering to disconnect the sensor-minus tab from ground and re-route it to the micro:

Proto PCB Mods.jpg
Looks nasty but works fine, and the open-circuit detection works perfectly on the bench. So does the whole rig:

Wired Hardware.jpg
I'll be testing it open-board on the wife's Altie, just high-temp silicone sprayed on it for short-protection. That will be next weekend, I'm still waiting on stainless mending plates to modify for a bracket and some 5/16x3/8 hose reducers so I can remove the H-valve from the CVT cooling loop. The potting box in the pic is the one I intend to use, it's a Bud PB1581. The plan is to make a sandwich with the M5 mounting holes in the solenoid body, the potted board will fit on one side of the bracket and the solenoid on the other with the bracket in between. The final PCB will fit snugly into the box and have guide holes for steel spacers to be inserted during potting, so after potting and drilling the hole locations will exactly match-up with the solenoid. Should make for a setup that's compact and easy to build and assemble.

C-ya
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Re: Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

Postby C-ya » Sun Sep 25, 2022 6:33 pm

LOL on the jumpers. BTDT for engineers that the lab I worked in supported. Proof it then they can redesign the PCB. The lab instruments I work on now still have some production boards come through with jumpers.

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VStar650CL
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Re: Mountains, CVT, did the oil cooler install, still can't get uphill, now what?

Postby VStar650CL » Sun Sep 25, 2022 6:57 pm

C-ya wrote:
Sun Sep 25, 2022 6:33 pm
Proof it then they can redesign the PCB.
We generally call it a "spin" and for complex, expensive boards you definitely want to avoid them. But for a miniscule, 2-sided board like these, a spin is a $45 proposition. In this instance I pretty much counted on it, you notice there are no mounting holes. If you look close, I also left three of the unused pins on the micro with exposed test pads. The new detector circuit is soldered to the rightmost one in the pic. The other two may do temporary duty driving a red/green status LED if I discover any problems in operation on the car that require some "burn and learn" debugging.
:naughty:

Proto PCB Mod Pads.jpg


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